The present invention relates to a roller bearing which, by obtaining the optimum range of the undercut dimension of a flange portion of the roller bearing, not only can enhance the performance of the roller bearing such as seizure resistant property and low torque property but also enhances the workability of undercut grooves formed in the flange portion of the roller bearing to thereby be able to reduce the cost of the roller bearing.
In a tapered roller bearing, as shown in FIG. 1, between an outer ring 1 and an inner ring 2, there is rollably interposed a tapered roller 3 and, in the side portion of the inner ring 2, there is formed a flange portion 4 with which the end face of the tapered roller 3 can be contacted.
An axial load acting on the tapered roller bearing is supported mainly by the flange portion 4 and the end face of the tapered roller 3. Also, in the contact portion between the flange portion 4 and the end face of the tapered roller 3, there is formed a contact ellipse which can be calculated according to a Hertz contact theory. The contact ellipse varies according to the geometrical shapes of the flange portion 4 and the end face of the tapered roller 3 and a flange load acting on the flange portion 4.
Since the mutual contact between the flange portion 4 and the end face of the tapered roller 3 is rolling contact involving large sliding, when the quantity of lubricating oil to be supplied to the bearing is small, an oil film is hard to be produced between the flange portion 4 and the end face of the tapered roller 3, which raises a fear that friction and seizure can occur. Also, due to the fact that the present mutual contact involves sliding contact, great importance is attached to the low torque property of the bearing.
By the way, when grinding the raceway surfaces of the inner and outer rings 1, 2 as well as the flange portion 4, in order to prevent a grindstone from touching the boundary portion between the flange portion 4 and raceway surfaces, in the boundary portion, there is formed a undercut groove 5. However, there is a fear that such undercut groove 5 can have a serious influence on the seizure resistant property and low torque property of the bearing. That is, in case where the contact point between the flange portion 4 and the end face of the tapered roller 3 interferes with the undercut groove 5 and part of the contact ellipse formed due to mutual contact between the flange portion 4 and the end face of the tapered roller 3 is thereby caused to stick out into the undercut groove 5, in the vicinity of the boundary portion between them, there is produced an edge load. And, there is also a possibility that the edge load can have a value larger than the Hertz contact surface pressure obtained when part of the contact ellipse does not stick out into the undercut groove 5, which lowers the above-mentioned seizure resistant property and low torque property of the bearing.
In view of the above facts, conventionally, the undercut dimension c (FIG. 1) of the undercut groove 5 is controlled down to a sufficiently small value to thereby prevent the contact ellipse from interfering with the undercut groove 5, whereby the production of the edge load is avoided to thereby be able to prevent the lowered seizure resistant property and low torque property of the bearing.
However, it is very difficult to work the undercut grooves 4 in such a manner that the undercut dimension c is small for the following reasons: That is,
a. the size of a cutting tool for forming the undercut groove 5 of the flange portion 4 cannot be reduced so much because the strength and rigidity of the cutting tool must be secured;
b. it is necessary to secure the oscillation width of a grindstone;
c. when grinding the raceway surfaces of the inner and outer rings 1, 2 as well as the flange portion 4, it is necessary to prevent poor grinding such as unground portions and high edge portions due to unground;
d. it is necessary to allow variations in the finishing dimensions of the respective portions;
e. there is a limitation in a specially control for the working dimensions, because the production cycle and cost of the bearing are taken into account; and,
f. it is necessary to prevent the grindstone from being slackened due to thermal treatment deformation.
Especially, in a small-diameter bearing for use in a car, since the contact point height (in FIG. 1, h) between the flange portion 4 and the end face of the tapered roller 3 is close to the undercut dimension c in value, it is still further difficult to reduce the undercut dimension c.
For the above reasons, there h as been a demand that, without lowering the seizure resistant property and low torque property of the bearing, the undercut dimension c is set large to a certain degree to thereby facilitate the working of the undercut groove 4 so as to enhance the workability of the undercut groove 4 as well as reduce the cost of the roller bearing.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional roller bearings. Accordingly, it is an object of the invention to provide a roller bearing which, by obtaining the optimum range of the undercut dimension of a flange portion of the roller bearing, not only can enhance the performance of the roller bearing such as the seizure resistant property and low torque proper thereof but also enhances the workability of the undercut groove formed in the flange portion of the roller bearing to thereby reduce the cost of the roller bearing.
The above object can be attained by a roller bearing, according to the invention, which is structured such that between an outer ring and an inner ring, there are interposed a plurality of tapered rollers in a freely rollable manner, and a flange portion is formed in the side portion of the outer ring or inner ring, wherein the undercut allowance ratios of a contact ellipse formed due to contact between the flange portion and the end face of the roller are set in the range of xe2x88x920.6xe2x89xa6(h-b-c)/bxe2x89xa62, where (h-b-c)/b denotes the undercut allowance ratio, a grinding undercut dimension on the flange portion side is expressed as c, a contact point height between the flange portion and the end face of the roller is expressed as h, and the minor radius of a contact ellipse formed due to contact between the flange portion and the end face of the roller is expressed as b.
According to the invention, because the undercut allowance ratios of the contact ellipse are set in the above-mentioned range and also because there is obtained the optimum range of the undercut dimension of the flange portion, the undercut dimension of the flange portion can be increased to a certain degree without lowering the seizure resistant property or low torque property of the bearing. That is, by optimizing the undercut dimension in this manner, not only the performance of the bearing can be enhanced but also the workability of the undercut groove of the flange portion is enhanced to thereby be able to reduce the cost of the bearing.